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Subject[PATCH 2/4] Memory controller soft limit interface (v3)

From: Balbir Singh <balbir@linux.vnet.ibm.com>

Changelog v2...v1
1. Add support for res_counter_check_soft_limit_locked. This is used
by the hierarchy code.

Add an interface to allow get/set of soft limits. Soft limits for memory plus
swap controller (memsw) is currently not supported. Resource counters have
been enhanced to support soft limits and new type RES_SOFT_LIMIT has been
added. Unlike hard limits, soft limits can be directly set and do not
need any reclaim or checks before setting them to a newer value.

Kamezawa-San raised a question as to whether soft limit should belong
to res_counter. Since all resources understand the basic concepts of
hard and soft limits, it is justified to add soft limits here. Soft limits
are a generic resource usage feature, even file system quotas support
soft limits.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---
include/linux/res_counter.h | 47 +++++++++++++++++++++++++++++++++++++++++++
kernel/res_counter.c | 3 +++
mm/memcontrol.c | 20 ++++++++++++++++++
3 files changed, 70 insertions(+), 0 deletions(-)

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 4c5bcf6..b5f14fa 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -35,6 +35,10 @@ struct res_counter {
*/
unsigned long long limit;
/*
+ * the limit that usage can be exceed
+ */
+ unsigned long long soft_limit;
+ /*
* the number of unsuccessful attempts to consume the resource
*/
unsigned long long failcnt;
@@ -85,6 +89,7 @@ enum {
RES_MAX_USAGE,
RES_LIMIT,
RES_FAILCNT,
+ RES_SOFT_LIMIT,
};

/*
@@ -130,6 +135,36 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
return false;
}

+static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
+{
+ if (cnt->usage < cnt->soft_limit)
+ return true;
+
+ return false;
+}
+
+/**
+ * Get the difference between the usage and the soft limit
+ * @cnt: The counter
+ *
+ * Returns 0 if usage is less than or equal to soft limit
+ * The difference between usage and soft limit, otherwise.
+ */
+static inline unsigned long long
+res_counter_soft_limit_excess(struct res_counter *cnt)
+{
+ unsigned long long excess;
+ unsigned long flags;
+
+ spin_lock_irqsave(&cnt->lock, flags);
+ if (cnt->usage <= cnt->soft_limit)
+ excess = 0;
+ else
+ excess = cnt->usage - cnt->soft_limit;
+ spin_unlock_irqrestore(&cnt->lock, flags);
+ return excess;
+}
+
/*
* Helper function to detect if the cgroup is within it's limit or
* not. It's currently called from cgroup_rss_prepare()
@@ -178,4 +213,16 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
return ret;
}

+static inline int
+res_counter_set_soft_limit(struct res_counter *cnt,
+ unsigned long long soft_limit)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&cnt->lock, flags);
+ cnt->soft_limit = soft_limit;
+ spin_unlock_irqrestore(&cnt->lock, flags);
+ return 0;
+}
+
#endif
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index bf8e753..4e6dafe 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -19,6 +19,7 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent)
{
spin_lock_init(&counter->lock);
counter->limit = (unsigned long long)LLONG_MAX;
+ counter->soft_limit = (unsigned long long)LLONG_MAX;
counter->parent = parent;
}

@@ -101,6 +102,8 @@ res_counter_member(struct res_counter *counter, int member)
return &counter->limit;
case RES_FAILCNT:
return &counter->failcnt;
+ case RES_SOFT_LIMIT:
+ return &counter->soft_limit;
};

BUG();
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7bb14fd..75a7b1a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1939,6 +1939,20 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
else
ret = mem_cgroup_resize_memsw_limit(memcg, val);
break;
+ case RES_SOFT_LIMIT:
+ ret = res_counter_memparse_write_strategy(buffer, &val);
+ if (ret)
+ break;
+ /*
+ * For memsw, soft limits are hard to implement in terms
+ * of semantics, for now, we support soft limits for
+ * control without swap
+ */
+ if (type == _MEM)
+ ret = res_counter_set_soft_limit(&memcg->res, val);
+ else
+ ret = -EINVAL;
+ break;
default:
ret = -EINVAL; /* should be BUG() ? */
break;
@@ -2188,6 +2202,12 @@ static struct cftype mem_cgroup_files[] = {
.read_u64 = mem_cgroup_read,
},
{
+ .name = "soft_limit_in_bytes",
+ .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
+ .write_string = mem_cgroup_write,
+ .read_u64 = mem_cgroup_read,
+ },
+ {
.name = "failcnt",
.private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
.trigger = mem_cgroup_reset,
--
Balbir


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